Objects such as beans, grains, fruits and similar small-sized objects have been generally sorted using optical sorting apparatus. The objects pass through the apparatus where they are irradiated by visible light, ultraviolet light, infrared light, or other electromagnetic radiation such as microwaves. A detector generates an electric signal derived from light reflected from the object. If the sorting is based either in whole or in part on the color of the object, then at least two detectors produce electrical signals related to light reflected from the object and detected by the detectors. Electronic circuitry processes the signals from the detectors and determines if the object should be or rejected by additional apparatus in the sorting device.
Many prior art sorting systems reject objects based upon color alone. Specifically, nominally identical light signals are directed to photo detectors whose response characteristics peak in different areas of the light spectrum. Thus, the output signal from each detector indicates the reflectance of: the object at the wavelengths at which the detectors peak. The various outputs are compared and, based upon a reference value, a decision whether to accept or reject the object is made. For example, if the object had an unacceptable color, the reflectance of the object at a certain wavelength would be below the reference value. The apparatus would then output a signal to a rejecting mechanism to have the particular object rejected.
U.S. Pat. No. 4,057,146 is an example of such a prior art sorting apparatus. Objects fall one at a time through a ring of detectors in which light is reflected off each object. Light at the predetermined wavelength or two colors of light is detected and processed, and a rejecting mechanism activated if the object has an unwanted color or if the object is too small. To prevent generating spurious signals, the electronic quality analysis apparatus is self-synchronized, in that synchronizing signals are derived from the signals generated by the reflecting light itself. This apparatus should not be enabled when an object is not in the analysis zone. Similarly, the rejecting apparatus, which is activated by a rejection signal generated by the analyzing apparatus, should not be enabled when an object is not in the analysis zone.
A problem with this prior sorting apparatus sorts based on color is that very dark objects are difficult to detect. A black body, by definition, absorbs all light so little, if any, light is reflected from such a body. Thus, a black object that should be rejected passes through the sorting apparatus undetected, and reduced the effectiveness of the sorting apparatus. This is particularly a problem when black beans need to be sorted out of lighter color beans.
It will therefore be appreciated that a significant need exists for a sorting apparatus which is able to sort very dark colored objects from light color objects. The present invention fulfills this need, and further provides other related advantages.